1. Field of the Invention
This invention relates in general to a protective circuit for preventing burn-in spots on the picture screen of a display device.
2. Description of the Prior Art
A normal circuit arrangement is provided in the scanning electron microscope identified as the Cambridge Stereoscan model S150. When the electron beam in this apparatus is positioned by means of an external drive of the deflection system in the spot mode then this circuit causes an additional deflection of the electron beam in the visual display along a small circle. This prevents a picture element selected over a longer time span from being destroyed or damaged due to receiving too high a dosage of energy. The intensity control of the electron beam by luminosity information received from the microscope column is cancelled in this mode and is replaced by an adjustment of the visual display to a constant luminosity of the circle which is being produced. With such system, the visual presentation of a specimen which is being investigated with the scanning electron microscope is not possible on the picture screen in the spot mode.